Tool_maker; My brother is an auto mechanic. He often tells me stories about other mechanics changing parts indicated by the error code, but not fixing the problem. The first thing he asks is if they pulled all of the codes, not just the first one that popped up. Then did they look at the fault table to see what the combination of codes indicated. Then, decide which part is most likely, easiest to change , and the cheapest.

I had a rental car that had the engine warning light come on the first day. I found out previously that a loose gas cap can cause an emissions code, which turns on the engine fault light. Since the car ran fine, I checked the gas cap, and continued to use it, waiting for the fault to reset itself - it finally did on the 3rd day.

@GlennA: I probably do not remember every auto repair I ever had or every mechanic who has worked on one of my cars/trucks. That said, it does seem as though today if there is not a computer code stored somewhere, the mechanic has no idea of what the trouble is. It is really cool when a machine can be plugged in and tell the mechanic that X, Y or Z has failed and therefore needs to be replaced, but it is absolutely frustrating when my truck keeps dying, at any speed, and none of the five garages I took it to (including two dealers) have any idea why because there was no computer code to tell them.

As far as machines fixing themselves, I can visualize rare occasions where a machine could bypass a faulty circuit, but unless it includes a welder and spare parts I do not see how it is even remotely possible.

Diagnostic messages tell what the designer thinks is happening. Machines don't lie to be malicious, but because they are dumb. When I hear that machines will be able to fix themselves, I don't believe it. A machine can't tell if a sensor is detecting a problem, or if the sensor has failed. Part of troubleshooting is thinking like the machine - recognizing what sensors the machine has and what it can, or can't, detect.

From this discussions, it appears that more than a few of the folks who post here are DIY mechanics as well as technocrats. So they are well aware of how enjoyable - and increasingly rare - it is to find a machine which has been deliberately designed for easy diagnosis and repair.

I'm aware that in my own career I've designed devices that were appreciated for their excellent serviceability.....as well as some which were frankly terrible. We can probably all recall presenting finished designs which worked, but which needed improvement right from the start..... if only we had a bit more time.

Thinking back on my own education, I don't believe that the idea of designing for serviceability was ever considered. I wonder why? Aren't some of the basic features of a serviceable part quite simple? And possibly even universal?

Seems like going to a dealership or auto shop for repairs is like calling for computer tech support. The person assigned to your ticket may never have done the hands on trouble shooting and is simply following a troubleshooting "tree". You can also pay an automotive tech less than you can pay a "real" mechanic. None of this bodes well for the customer, unless you really have a good component level knowledge of the misbehaving system.

When I had my shop, there were "parts changers" all over the place. That's where I got most of my business. They couldn't figure out the problem, the customer was getting upset about the cost for them guessing, and they would finally recommend the "electrical specialist". The first thing I would do when I got a car to repair was disregard all the other repair work that was done and start from scratch. There was more than one time when a previous "repair" had actually created a more complex issue as there was now more than one problem with the vehicle.

rScotty, the cars I am talking about I knew inside and out. I had the original shop manuals and had taken apart and rebuilt just about everything. I had a great house with an attached garage and a good place to pull engines. I had an unfinished basement and there were often a couple of engines being worked on there. I could change and engine or replace the clutch or differentail by myself in a day eaisly. Even so, there would be problems for which there was no easy answer.

This story of the TOWN CAR reminds me of a poser from several decades before that. We had a 1960 FORD GALAXIE, with a 223 C.I.D 6-cylinder engine. After about 6 months, the engine developed a prolonged whistle during the deceleration time. The dealer couldn't figure out the problem. They changed the intake/exhaust manifolds gasket, the gasket to the carburetor, the asbestos gasket to the engine exhaust pipe from the manifold ... all to no avail. As I recall this was late in the work week. They scheduled a factory troubleshooter to come in the following week to inspect the problem & offer a solution. In the meantime, we took the vehicle back home, and continued to drive it since it was a needed means of transportation. On that Saturday, I got out my own wrenches and tackled the job. After listening intently for the source of the whistle while revving the engine in the driveway, I decided to remove the intake/exhaust manifold for a closer look. There was a set of expansion nipples compressed between the cylinder head & the manifold. Squeezing them with a CHANNELOCK pliers, I removed each one individually, inspected them, and set them aside. Then I looked at the head & the manifold closely using a hand-held magnifying glass. After NOT seeing anything pop out, I reinserted each one of these "nipples" into the cylinder head, and (using the same manifold gasket ) reinstalled the manifold and all the associated parts & bracketry. I started the engine, and notice NO whistle. So, I cleaned up, and went for a ride in the neighborhood. NO whistle! Then I went onto a main drag where I could accelerate & decelerate to highway speeds..... NO whistle! On Monday, I called the FORD dealer to tell him I solved the problem. When the service manager asked me WHAT I had done, I declined comment. I figured that since their mechanics (that's what they were called in 1960!) couldn't solve the problem, I sure as heck wasn't going to give them any heads-up. After 4 years of reliable oepration, we sold the car to our neighbor's friend, who continued to drive it for several more years, until it was damaged in an accident.

Conclusion: Although I was NEVER certain, my conclusion was that at least one of those nipples was improperly installed inside the head, causing an air leak which caused the whistle during deceleration when the vacuum in the manifold is at a maximum. Removing & reinstalling them, maybe was just what they needed to be properly positioned to eliminate the leak.

And: I also concur with some of the comments about the state of auto technology today, AND the state of the auto dealerships. While they seem willing to sell a car literally for pennies over their actual cost, when it comes to routine maintenance AND/OR required service, they have their fangs out to grab every last dollar in your wallet (or credit card!)

Presently we have a CAMRY. This past Spring, it developed a growl in the rear. It was diagnosed as a defective rear wheel bearing. From time of diagnosis to time of delivery was no more than ONE HALF hour ..... YET the bill to change it was about $600.!!! Darn good thing we have 100K protection plan. Since the CAMRY is front wheel drive, changing a rear wheel bearing IS a snap! There's NO powertrain components to get in the way!

Charles, I'm not so sure that with all of the new diagnostics you are more likely to find the real culprit. Yes, diagnostics are improving, but with the addition of new embedded PC's, more uC's, wiring harnesses, etc., the complexity is increasing even faster. At some point, if the diagnostics do keep up, with the complexity of all the sensors to check the sensors, a failure is as likely to be in the diagnostics as in the actual functional parts of the machine.

My experience with older cars is to work on them myself, if I can. Most times, technicians follow the script rather than diagnose, which is an expensive venture (but profitable for them). Even worse, if they are not careful, fixing one problem will break a different (but perhaps marginal) part, leading to having to bring it back.

My wife's 1994 had problems with its AC a couple weeks after taking it to the dealer for another problem (but that required touching the AC to fix). After being told we needed a new compressor (without any guarantee that it would be fixed) as the first step in the diag. process, I stopped by and talked the tech thru a better diagnostic process. Would up fixing it for much less (and the dealership absorbed half the cost).

Since many dealers turned their repair facilities into individual profit centers, repair costs have increased significantly. Usually a garage or repair facility charges less and for most jobs the technicians are equally qualified. However: When they buy a part from a dealer, electronics in particular, you own it! This makes trial and error repairs extremely expensive. A dealer repair center can take parts out of stock, try them and return them to stock with only the labor charge to install and remove them. As cars become more and more integrated with electronics, hydraulics, pneumatics, and mechanical assemblies, the consumer needs to excercise discression regarding who they hire to fix certain problems. Sometimes (!) the dealer is the best choice.

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.